Hermann Hagedorn (1882, New York City – d. 1964) was an American author, poet and biographer.

He was born in New York City and educated at Harvard University, the University of Berlin, and Columbia University. From 1909 to 1911, he was an instructor in English at Harvard.

Hagedorn was a friend and biographer of Theodore Roosevelt. He also served as Secretary and Director of the Theodore Roosevelt Association from 1919 to 1957. Drawing upon his friendship with Roosevelt, Hagedorn was able to elicite the support of Roosevelt's friends and associates' personal recollections in his biography of TR which was first published in 1919 and then updated in 1921 and which is oriented toward children. The book has a summary questions for young readers at the end of each chapter. Drawing on the same friends and associates of Roosevelt, Hagedorn also published the first serious study of TR's experience as a rancher in the Badlands after the death of his wife and mother in 1884. Hagedorn's access to TR's associates in these two books has been utilized by historian, Edmund Morris in his two highly acclaimed biographical books on Roosevelt published in 1979 and 2001.
--Wikipedia